1. Field of the Invention
The field of the invention is neuronal death such as that which occurs during neurodegenerative diseases, and following stroke or trauma. The invention identifies a novel biochemical mechanism required to induce death in neurons from a variety of neurotoxic insults.
2. Description of the Related Art
Neuronal death underlies symptoms of neurodegenerative diseases (ND) and damage from stroke and trauma. Neuronal death in neurodegenerative diseases such as Alzheimer's Disease (AD) and Parkinson's Disease (PD) is characterized by a number of features, including: (a) memory loss; (b) language deterioration; (c) impaired motor skills; (d) poor judgment; and (e) indifferent attitude. Although AD usually begins after age 60, its onset may occur as early as age 40. AD first appears as memory decline. As the disease progresses over several years, cognition, personality, and the ability to function are all impaired or destroyed.
There is no cure for AD and no way to slow the progression of the disease. For some people in the early or middle stages of the disease, medication such as tacrine may alleviate some cognitive symptoms. Also, some medications may help control behavioral symptoms such as sleeplessness, agitation, wandering, anxiety. and depression. These treatments are aimed solely at making the patient more comfortable and do nothing to slow the progression of the underlying neuronal death in the disease.
As such, there is much ongoing research that is aimed at the identification and development of new therapeutic agents which can at least slow, if not reverse, the death of neurons in AD and other neurodegenerative diseases or following stroke or trauma.
An important tool in the identification of therapeutic agents for neuronal death would be the development of an in vitro model of neuronal death, which would replicate the biochemical steps involved in the death process. Such an in vitro model would be invaluable for screening and developing potential therapeutic agents.
As such, there is intense interest in the development of a practical in vitro model for neuronal death, one which would exhibit biochemical features common to diverse stimuli.
In view of the intense interest in the development of practical neurodegenerative disease models, a number of mouse models for AD and PD have been developed to date. Despite the number of different mouse models that have been developed, no one animal model demonstrates the marked neuronal death accepted as being completely correlative of the degenerative disease condition. Thus, the biochemical mechanisms which underlie human ND disease and stroke related neuronal death are poorly understood.
Therefore, there is great interest in the elucidation of the signal transduction pathway which underlies neuronal death. This invention identifies a biochemical pathway used by all neurons in response to diverse neurotoxic stimuli. As such, it enables in vitro neuronal models which demonstrate reliable, reproducible neuronal death to be used as screens for compounds which would inhibit steps in the novel biochemical pathway. Such a model would greatly facilitate the identifications of compounds which could be used to alleviate human neuronal disease.
Cells throughout the body are dependent upon the ability of membrane receptors to bind ligands and to effectively signal a cascade of biochemical events from the membrane to the nucleus. In the immune system, ligand binding to receptor (i.e. antigen to antigen receptor) induces changes in the morphology of the cell through cytoskeletal reorganization and induces the nucleus to activate the transcription of new genes to promote cellular differentiation and/or proliferation. This change in cell morphology is known as capping and refers to a polarization process in which cell surface proteins migrate to a specific pole of the cell (Taylor et al., 1971). The molecular mechanism of capping is poorly understood. It is clear, however, that disruption of the polarization process disrupts immune signaling (Bourguignon and Bourguignon, 1984).
The plasma membrane of lymphoctes has recently been shown to contain discrete lipid microdomains referred to as “lipid rafts” (Parton and Simons, 1995; Bromley et al., 2001). The terminology lipid rafts indicates microdomains of the plasma membrane which were first identified based on their insolubility in certain nonionic detergents and are enriched in glycosphingolipids and cholesterol. This work has shown that the plasma membrane is not a uniform lipid bilayer but rather that it contains specialized lipid microdomains which act as signaling platforms for the transduction of external signals into cellular responses. The aggregation of lipid rafts is essential for signaling in cells throughout the body. Disruption of lipid raft aggregation through the use of inhibitors of lipid raft assembly (i.e. cholesterol depleters) abrogates cell signaling. The relationship between capping and lipid raft aggregation has been unclear but recent evidence demonstrates that signal transduction involves the selective movement of key signaling proteins into and out of lipid rafts organizing a signaling module. In the immune sytem, this signaling module has been termed the immunological synapse to describe the site of cell-cell contact between communicating immune cells. Such spatial contact and communication (i.e. cell-cell co-capping) is essential for all immune functions. Khan et al., 2001 provided evidence for the polypeptide agrin as the first endogenous mediator of immune polarization and lipid raft aggregation. This was the first description of an endogenous lipid raft assembly inducing protein. The applicant reasoned that the polarization of raft microdomains may be a conserved mechanism of biological signaling used by neurons for signal transduction. This invention describes the polarization of raft microdomains on the cell body/soma of neurons in response to external stimuli. It demonstrates that polarization of raft microdomains is a signal transduction mechanism utilized by a variety of neurotoxic stimuli during death signaling.